The mouse t-complex on chromosome 17 has long been a focus of interest for developmental biologists. Because many embryonic lethal mutations are localized in the region, corresponding genes of importance during development are inferred to reside there. It is thus a prime target for high priority analysis. We have completed and verified a Sequence Tagged Site (STS) /Bacterial artificial chromosome (BAC)-based physical map. It represents about half of the estimated 30 Mb t-complex in 450 BACs fitted with 650 STSs and integrating many of the short tandem repeat markers used in genetic mapping. Forty-three selected BACs were sequenced, most in conjunction with the Mouse Genome Consortium. The sequences independently verify and augment whole genome shotgun sequencing, including the provision of sequences that fill otherwise open gaps. We have analyzed and provided a curated annotation merged and incorporated into public databases that provides candidate genes and clones to 1) identify various t-complex embryonic lethal mutations in conjunction with collaborating laboratories, and 2) investigate critical processes in early development. Our collaborator Dr. K. Abe is currently focusing on the search for the gene mutated in the tw5 embryonic lethal. Histological studies have demonstrated that mice homozygotic for tw5 die at the gastrulation stage due to extensive death of the embryonic ectoderm cells, which fail to aggregate. BAC transgenes have shown that the most distal BAC mapped to the critical region rescues the tw5 lethality, restoring viability. An effort to identify the specific gene within the BAC is now in progress. This approach could potentially be expanded to other t-complex lethal loci as well, based on the refined map of the region. Several metalloproteases have critical roles in cell-cell signal transduction, and the gene ADAMTS-10, a zinc metalloendopeptidase with thrombospondin domains, maps to the tw5 critical region (about 600 Kb). This gene is a potential candidate for important functions during development based on its structural domains. Recently its human homologue was found to be a candidate gene for Weill-Marchesani syndrome (OMIM#277600). We have found that mouse ADAMTS-10 is alternatively spliced in a tissue-specific manner, and alternative splicing results in protein isoforms that either include or exclude the thrombospondin domains. We have cloned and characterized 3 major isoforms from embryo, kidney and lung and find that the embryo, for example, expresses an isoform that has a truncated translation product. Selective regions of the protein specifically retained in different isoforms are being fused to maltose binding protein to raise antibodies, which will then be used to directly assess the expression pattern of different isoforms during development.